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Showing 3 results for Ghodousi


Volume 18, Issue 3 (9-2018)
Abstract

Self-compacting concrete as a type of concrete that has no need to vibration can use for complicated frameworks and in conditions that compaction is hard. So this concrete is an excellent choice for repair and retrofitting of many kinds of concrete structures such as marine structures, bridges and so on. These concrete structures may be under aggressive environmental conditions and harmful agents. One of the most important damages of concrete structures is because of freezing and thawing cycles especially in exposed ones, like bridge’s decks. So, study of effect of different parameters on quality of self-compacting repair layer, its bonding to substrate and its durability under chemical and physical attacks is very important. In this study, effect of paste volume, water to cementitious materials and polypropylene fiber dosages in mix design on rheological, hardened properties and bonding of repair fiber-reinforced self-compacting concrete (FRSCC) to concrete substrate and its durability for freezing and thawing cycles has been assessed. Bonding between FRSCC as a repair layer and concrete substrate had been evaluate using pull-off test. The tests that failed exactly from the bond surface considered as a successful ones, and all tests that failure had been occurred in repair layer or concrete substrate is eliminated from the results. Freezing and thawing test was conducted according to ASTM C666. Both freezing and thawing processes were made in water. To assessment of bonding of FRSCC as a repair layer to concrete substrate, we made 15 cm cubes of substrate layer with compressive strength more than 50 MPa to ensure that the failure doesn’t occur in this layer while pull-off test. After six months (to have concrete substrate without shrinkage),we saw the cubes divided them to 3 pieces. With analyzing of effects of fiber dosages on rheological properties of the mix designs, we found that an increase in fiber percentage that leads to smaller diameter in slump flow test, higher flow time in T50 test, higher time in V-Funnel test, and lower ratio in L-Box test. Also, while compressive strength had no significant changes, tensile strength and modulus of elasticity experienced a big increase through adding polypropylene fibers. Shrinkage of repair layer had a great decrease after adding polypropylene fibers. The optimum dosage of polypropylene fibers for hardened properties of the mix designs was found 0.1% by volume. We can see that because of the positive effect of fibers on decreasing of shrinkage and increasing of tensile strength of repair layers, bonding between the repair layer and concrete substrate increased greatly especially by adding 0.1% polypropylene fibers (by volume). Also, increase of paste volume and water to cementitious materials (summation of cement and micro silica) had negative effect on bonding of repair layer to substrate. That is because of increase of shrinkage of repair layer. Although, adding polypropylene fibers improved bonding of repair layer and substrate in freezing and thawing cycles, we see smaller results for bonding. We defined debonding index (DI) that presents the rate of debonding during freezing and thawing cycles. Higher DI, higher rate of debonding. As we can see, for mixes that containing polypropylene fibers, DI is bigger in comparison with the ones without them.

Volume 19, Issue 4 (winter 2019 2019)
Abstract

Many studies have confirmed the acceleration of economic growth through financial development, but just a few studies have discussed the disproportionate effect of financial development on the growth of the firms with different sizes. So the distributional effects of financial development among firms are still unclear. Accordingly, using a dynamic panel model, we have examined the role of small firms in different industries on the effect of financial development on industrial development of Iranian economy. This study has been carried out on 22 industries according to ISIC4 two-digit codes for the period 1383-1393 (Iranian Calendar) using the Generalized Moment Method (GMM). The results of the model confirm that the development of financial intermediaries exerts a positive effect on the industries with a bigger technical share of small firms. In other words, financial development through banking development has a more positive effect on small firms than large firms. This result is not valid for the development of the stock market.

Volume 26, Issue 4 (Winter 2023)
Abstract

Today, due to the rapid growth in population, many problems have arisen such as a lack of, and improper spatial distribution of urban services. Therefore, the purpose of this research is to evaluate accessibility in Bojnourd city by considering key land uses with different travel modes. In this research, 6 key land uses have been identified and accessibility to three modes of travel on foot, bus, and taxi have been obtained for each of the land uses using the two-stage floating catchment area (2SFCA) method. Also, based on the usage of each travel mode, their relative weight is obtained. Then, the integrated accessibility for each land uses is obtained based on three travel modes. Also, using the DANP method, the weight of each land use was obtained and the integrated accessibility map was obtained using the weighted linear combination (WLC) method. Based on the weighing results, green spaces and educational land uses have been the most important. According to the final accessibility, the central and southern parts of the city and the township located in the east of the city have favorable accessibility whereas other areas have unfavorable accessibility. Based on the results, we can conclude that vertical spatial justice has not been observed in Bojnourd city; because the neighborhoods that do not have a good social and economic level, lack good level of accessibility.


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